The present invention relates to a cigarette filter that includes a smoke constituent adsorbent which, when combined with a carbon-based filtering material, demonstrates synergistic reductions in smoke vapor constituents.
Cigarettes include tobacco rods or columns which, when burned, produce a particulate and a vapor phase. About 70 years ago, filters began to be attached to an end of the tobacco column. Among other things, the filter removed various smoke components. Filters made from filamentary or fibrous material, such as cellulose acetate tow or paper, remove the particulate phase of tobacco smoke by mechanical means. However, the fibrous materials are not effective at removing volatile constituents, such as aldehydes, hydrogen cyanide and sulfides, which are found in the vapor phase. Typically, an adsorbent or absorbent is combined with the fibrous material to improve removal of the vapor phase components. For example, cigarette filters have included activated carbon, porous minerals such as meerschaum, silica gel, cation-exchange resins and anion-exchange resins.
Charcoal has a high specific surface area and is a relatively strong adsorbent for vapor-phase constituents of tobacco smoke. When coated with a mixture of metallic oxides, charcoal is particularly effective in removing acidic gases. Meerschaum has a large adsorption area with a strong adsorption affinity for charged species, but a considerably low adsorption affinity for non-polar species. Silica gels are generally regarded as weakly retentive adsorbents for vapor-phase constituents of tobacco smoke. Although silica gel readily adsorbs aldehydes and hydrogen cyanide, the constituents also readily desorb from the silica gel. Cation exchange resins have been proposed for nicotine removal. Anion exchange resins have been proposed for the removal of smoke acids, but strongly basic anion exchangers have no effect on smoke vapor phase aldehydes. Weakly basic anion-exchange resins of porous structure are suitable for the removal of smoke acids and aldehydes, but their efficiency diminishes during smoking, as does that of carbon and porous minerals.
Two or more adsorbents can be used in combination in cigarette filters. For example, U.S. Pat. No. 2,815,760 describes the use of an ion exchange material with materials which xe2x80x9cchemically react with the harmful, nonalkaline and nonacid components of the smoke to form non-volatile compounds, thus retaining the latter to the filter.xe2x80x9d However, the aforesaid additives have not yielded satisfactory selective removal of such smoke phase components, as smoke aldehydes, particularly acetaldehyde and acrolein. U.S. Pat. No. 4,300,577 describes the use of a weakly retentive absorbent for vapor-phase constituents intermingled with a second component having mainly primary amino functional groups for the removal of vapor-phase constituents, including aldehydes and hydrogen cyanide from tobacco smoke. However, the filter of the ""577 patent has not been shown to demonstrate adequate consumer acceptance or commercial viability.
The present invention relates to a cigarette filter that includes a multiple section filter which reduces the level of predetermined smoke constituents. The filter consists of a fibrous filter plug located at the mouth-end of the cigarette, a section containing a selective adsorbent material, and a section containing a general adsorbent material.
The filter plug can be any filter plug known in the art, such as cellulose acetate tow. The general adsorbent material is preferably selected from a group of relatively high surface area materials, such as activated charcoal, which are capable of adsorbing a range of chemical compounds without a high degree of specificity. The selective adsorbent material is chosen based on the specific smoke constituents targeted for removal. Preferably, the selective adsorbent material is selected from a group of surface functionalized resins, wherein each resin consists of an essentially inert carrier with a surface area of greater than about 35 m2/g. In an embodiment of the present invention, the selective adsorbent material has a phenol-formaldehyde resin matrix surface-functionalized with mainly primary and secondary amine functional groups.
Structurally, the selective adsorbent material may be positioned adjacent to a tobacco rod and the general adsorbent material positioned between the selective adsorbent section and the filter plug. Alternatively, the general adsorbent material may be positioned adjacent to the tobacco rod and the selective adsorbent material positioned between the general adsorbent section and the filter plug. Preliminary data indicates that the former orientation produces a synergistic effect in smoke constituent reductions relative to the latter orientation. Further, the selective adsorbent and general adsorbent may be interspersed in a traditional filter plug material, such as cellulose acetate, or the adsorbents may be packed as a bed or thin layer sections within filter plug material.